System including a heat exchanger with different cryogenic fluids therein and method of using the same

ABSTRACT

A system can include a heat transfer structure and a heat exchanger. The heat transfer structure is to cool an object, and the heat exchanger is to cool a portion of the heat transfer structure. The system can be cooled significantly faster than a conventional system that uses conductive cooling. The system has no or less liquid cryogen that would be vaporized as compared to a conventional system that immerses the object to be cooled within a bath of liquid cryogen or has a substantial mass of liquid cryogen within a cooling loop.

BACKGROUND

1. Field of the Disclosure

The disclosure relates to systems, and methods, and more particularly tocooling systems including heat exchangers with different cryogenicfluids therein and methods of using the systems.

2. Description of the Related Art

A conventional low-temperature superconducting system can be cooled byimmersion, convection, or conduction. Conventional immersion cooling ofa cryogenic system can include using a liquid cryogen. FIG. 1 includes aschematic drawing of a conventional magnetic resonance imaging (“MRI”)system 100 that includes a superconducting coil 190 that is containedwithin a vessel 140. The vessel 140 has an outer wall 142, an inner wall144, and a thermal shield 182 disposed therebetween. An interior space160 is disposed within the inner wall 144. The vessel 120 can includeanother wall 172, a patient wall 174 with a space 176 in which a patient(not illustrated) may be placed when using the MRI system 110 duringnormal operation.

The MRI system 100 is cooled by condensing gaseous cryogen into a liquidcryogen by the use of a cryocooler 120. More particularly, gaseouscryogen, which lies above line 170, is condensed, and thesuperconducting coil 190 is at least partially immersed within a bath ofliquid cryogen (below line 170), such as He.

As can be seen in FIG. 1, a significant amount of the interior space 160within the interior wall 144 is filled with liquid cryogen. Althoughcoils can be provided to customers with the cryogen installed, it iscommon for routine service and expected failure modes to deplete some ofthat cryogen. Many areas of the world do not have ready supply ofreplacement liquid cryogen or an equivalent high purity gas. Therefore,a magnet system with limited or no liquid cryogen is desirable.

A dual-phase, convective cooling loop is described in U.S. Pat. No.5,461,873. A superconducting coil is disposed within the dual-phasecooling loop. The superconducting coil is cooled by boiling the liquidcryogen within the dual-phase cooling loop. Thus, the system has asubstantial amount of liquid cryogen that is thermally connected to thesuperconducting coil. The dual-phase, convective cooling loop suffersfrom the same problem as the immersion cooling. A quench can cause allliquid cryogen to become vaporized and exhausted from the system. Again,the system will need to be recharged with cryogen after a quench occurs.

For conduction cooling, only minimal amounts of liquid cryogen are used.A cooling source, such as a cryocooler, has a cold surface in contactwith a surface of an object that is to be cooled, such as asuperconducting coil. As compared to convective cooling, the conductivecooling is very slow.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1 includes a schematic drawing of a magnetic resonance imagingsystem. (Prior art).

FIG. 2 includes a schematic diagram of a superconducting system inaccordance with an embodiment described in more detail below.

The use of the same reference symbols in different drawings indicatessimilar or identical items. Skilled artisans will appreciate thatelements in the figures are illustrated for simplicity and clarity andhave not necessarily been drawn to scale.

DETAILED DESCRIPTION

A system can include a heat transfer structure and a heat exchanger. Theheat transfer structure is to cool an object, and the heat exchanger isto cool a portion of the heat transfer structure. The system can becooled significantly faster than a conventional system that usesconductive cooling. The system has no or less liquid cryogen that wouldbe vaporized as compared to a conventional system that immerses theobject to be cooled within a bath of liquid cryogen or has a substantialmass of liquid cryogen within a cooling loop. Thus, the system is morelikely to withstand a fault or other undesired condition without havingto recharge the system with a cryogen.

A few terms are defined or clarified to aid in understanding of theterms as used throughout this specification. As used herein, the term“coupled” is intended to mean a connection, linking, or association oftwo or more components, sub-systems, or any combination thereof in sucha way that a fluid or energy may be transferred from one to another.Coupling may be direct or indirect. For example, thermal coupling caninclude a direct contact between a cold surface and an object to becooled, or an indirect thermal connection in which an object is cooledby a first medium, which in turn is cooled by a second medium, whereinthe second medium does not contact the object (i.e., the object isthermally coupled to the first medium). Coupling can include thermalcoupling, fluidal coupling, mechanical coupling, etc.

The term “typical operating state” is intended to mean a state in whichall superconducting elements along a superconducting current path are intheir superconducting states.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

Additionally, for clarity purposes and to give a general sense of thescope of the embodiments described herein, the use of the “a” or “an”are employed to describe one or more articles to which “a” or “an”refers. Therefore, the description should be read to include one or atleast one whenever “a” or “an” is used, and the singular also includesthe plural unless it is clear that the contrary is meant otherwise.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. All publications, patentapplications, patents, and other references mentioned herein areincorporated by reference in their entirety. In case of conflict, thepresent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and notintended to be limiting.

To the extent not described herein, many details regarding specificmaterials, processing acts, and components, assemblies, and systems areconventional and may be found in textbooks and other sources within thesuperconducting, cryogenic, and medical device arts.

While much of the description herein is directed to an MRI system, afterreading this specification, skilled artisans will appreciate that theconcepts described herein may also be extended to a different system. Inanother embodiment, the system may include a superconducting element ina different application (e.g., a transmission or distribution cable, atransformer, a fault current limiter, one or more other suitableelectronic devices, or any combination thereof). Thus, the systems andmethods described herein are not limited only for use with an MRIsystem.

Further, the concepts described herein are not limited tosuperconducting systems. The concepts can be extended to other systemsthat operate at temperatures no greater than about 110 K. A cryogen thatcan be used for such systems can include an elemental material (e.g.,He, Ne, Ar, etc.) or a molecular material (H₂, N₂, CH₄, etc.).

FIG. 2 includes a schematic of a system 200 in accordance with anembodiment. In one embodiment, the system 200 can be an MRI system. Inthe illustrated embodiment, nearly all of the components and sub-systemsare disposed within a vessel 202. Parts of a fill/vent line 274 and acoldhead 244 extend outside the vessel 202. In other embodiments (notillustrated), more, fewer, or different components, sub-systems, or anycombination thereof are disposed within or outside the vessel 202.

The system 200 includes a superconducting element 212 within the vessel202 that is evacuated. In one embodiment, the vessel 202 is operated ata pressure less than 10⁻³ Torr, and in another embodiment, less than10⁻⁵ Torr, 10⁻⁸ Torr, or even lower.

In the illustrated embodiment, the superconducting element 212 is anobject to be cooled by the heat transfer structure 220. Thesuperconducting element 212 is thermally connected to a portion 214 ofthe heat transfer structure 220 using a conventional or proprietaryconfiguration. In one embodiment, the superconducting element 212 caninclude a low-temperature superconductor. In a particular embodiment,the superconducting element 212 can include a superconducting coil, asuperconducting transformer, a superconducting switch, a superconductor(e.g., a wire, a terminal, a solder connection, etc.), or anycombination thereof. The superconducting element 212 can operate usingalternating current, direct current, ramped or pulsed signals, or anycombination thereof. If cooled with a liquid cryogen, thesuperconducting element 212 is at about the same temperature as theboiling point of a liquid cryogen used within the heat transferstructure 220. Thus, if He is used as the liquid cryogen, thesuperconducting element 212 may be cooled to approximately 4 K, if H₂ isused as the liquid cryogen, the superconducting element 212 may becooled to approximately 20 K, and if Ne is used is used as the liquidcryogen, the superconducting element 212 may be cooled to approximately27 K. If a gaseous cryogen is used, the superconducting element 212 canbe any temperature capable of being achieved at the operating pressureof the gaseous cryogen within heat transfer structure 220.

The heat transfer structure 220 includes the portion 214 that is coupledto another portion 234, via a portion 224. The other portion 234 of theheat transfer structure 220 is disposed within a heat exchanger 230. Theheat transfer structure 220 can include a single loop, a manifoldsystem, or the like. A cryogenic fluid flows within the heat transferstructure 220. The cryogenic fluid can operate by a thermosiphonprinciple, natural convection, or forced convection. The cryogenic fluidcan be any cryogen previously described herein. In one embodiment, thecryogenic fluid within the heat transfer structure 220 is in a singlephase state, such as a gas.

The cryogenic fluid within the heat transfer structure 220 can be at apressure such that sufficient cryogenic fluid is present to provideeffective cooling to the object being cooled (e.g., the superconductingelement 212) but not so high of a pressure that a significant amount ofliquid cryogen is present within the heat transfer structure 220. Thus,in one embodiment, the heat transfer structure 220 includes aprincipally single-phase cooling loop. In one embodiment, the pressureis in a range of approximately 0.5 to 100 atmospheres, and in aparticular embodiment, can be in a range of approximately 0.8 to 1.0atmospheres. Therefore, the pressure of the cryogenic fluid within theheat transfer structure 220 is at least three orders of magnitudedifferent from the pressure within the vessel 202. In anotherembodiment, the pressure difference is at least is at least six ordersof magnitude different, is at least nine orders of magnitude different,or even more.

In one embodiment, the cryogenic fluid enters the heat exchanger 230within portion 234 of heat transfer structure 220. The cryogenic fluidis cooled and becomes denser. The denser cryogenic fluid flows to andcools the superconducting element 212, which in turn heat the cryogenicfluid and makes it lighter (i.e., less dense). In one embodiment, thecryogen disposed within the heat transfer structure 220 remains in asingle state, even though its density changes. In another embodiment, agaseous cryogen disposed within the heat transfer structure 220 cancondense to form a liquid cryogen, and the liquid cryogen can bevaporized to form the gaseous cryogen.

The lighter cryogenic fluid disposed within the heat transfer structure220 flows to heat exchanger 230 (within the portion 234 of the heattransfer structure 220) and is cooled by a different cryogenic fluidwithin the heat exchanger 230, which in turn makes the cryogenic fluiddenser. In this manner, natural convention can be used to circulate thecryogenic fluid within the heat transfer structure 220 when the system200 is operating at steady state. In an alternative embodiment (notillustrated), forced convection can be used to circulate the cryogenicfluid within the heat transfer structure 220. To simplify understandingof the embodiments, the cryogenic fluid within the heat transferstructure may also be referred to as the “circulating fluid,” and thedifferent cryogenic fluid may also be referred to as the “buffer fluid.”

Within the heat exchanger 230, the circulating fluid within the heattransfer structure 220 is spaced apart and does not physically contactthe buffer fluid within the heat exchanger 230. The buffer fluid may bein a single phase state or more than one phase state. For example, thebuffer fluid can include a gaseous cryogen 236 and a liquid cryogen 238.The buffer fluid may have the same or different composition as comparedto the circulating fluid. In a particular embodiment, the buffer caninclude He that is in a gaseous state and a liquid state within the heatexchanger 230. The portion 234 of the heat transfer structure 220disposed within the heat exchanger 230 is immersed in liquid He. In oneembodiment, the portion 234 is partially immersed, and in anotherembodiment, the portion 234 is substantially completely immersed.

A coldhead 244 is coupled to the heat exchanger 230 via a wetsock 242.The coldhead 244 can have a single stage or more than one stage. Thecoldhead can include a Sterling cycle, Gifford-McMahon cycle, pulsetubes, or any other conventional or proprietary design. The wetsock 242can have a conventional or proprietary design. In a particularembodiment, the wetsock 242 can have a design and be used as describedin U.S. patent application Ser. No. 11/339,134, entitled “Method ofUsing a System Including an Assembly Exposed to a Cryogenic Region” byJones et al., filed Jan. 25, 2006. In another embodiment (notillustrated), a plurality coldheads and wetsocks similar to coldhead 244and wetsock 242, respectively, can be used.

When operating, the gaseous cryogen 236 can migrate from the heatexchanger 230 to the wetsock 242 and contact the coldhead 244. Thegaseous cryogen 236 can be condensed by the coldhead 244 into the liquidcryogen 238. In one embodiment, the amount of liquid cryogen 238 withinthe heat exchanger 230 is no greater than 100 liters, and in anotherembodiment, is no greater than 10 liters, or even smaller.

The design, size, and configuration of the heat exchanger 230 may dependon the amount of heat to be transferred, the space available within thevessel 202, the compositions and phase(s) of the buffer and circulatingfluids, the material separating the buffer and circulating fluids (i.e.,the material of the wall of the heat transfer structure 220), othersuitable consideration, or any combination thereof. After reading thisspecification, skilled artisans will appreciate how to design, size, andconfigure the heat exchanger 230 to meet their particular needs ordesires.

The system 200 can further include another heat exchanger 250, which isoptional. The heat exchanger 250 is thermally coupled to the coldhead244 and is thermally coupled to the heat exchanger 230, via a thermalswitch 262. In one embodiment, the heat exchanger 250 is permanentlythermally coupled to the coldhead 244. In another embodiment, the heatexchanger 250 is thermally connected to a different cooling stage ofcoldhead 244 other than a stage of the coldhead 244 to which the heatexchanger 230 is coupled. Each of the heat exchanger 250 and the thermalswitch 262 can include a conventional or proprietary design. In oneembodiment, a portion 232 of the thermal switch 262 is disposed withinthe heat exchanger 230, and another portion 252 of the thermal switch262 is disposed within the heat exchanger 250.

The heat exchanger 250 can be used to accelerate the rate of coolingdown the heat exchanger 230 during start-up of the system 200. Thedesign, size, and configuration of the heat exchanger 250 may depend onthe amount of heat to be transferred, the space available within thevessel 202, other suitable consideration, or any combination thereof.After reading this specification, skilled artisans will appreciate howto design, size, and configure the heat exchanger 250 to meet theirparticular needs or desires.

The thermal switch 262 can be closed during cooldown from warmertemperatures, and the thermal switch 262 can be opened before reachingsteady state. In one particular embodiment, the thermal switch 262 caninclude terminals (e.g., heat transfer surfaces) that are spaced apartfrom each other. The thermal switch 262 can be mechanical, gas-based, orother suitable design. For a gas-based switch, when the thermal switch262 is closed, a significant amount of gas fills the space between theterminals and allow a significant amount of thermal conduction betweenthe terminals. When the thermal switch 262 is open, the space betweenthe terminals is evacuated and substantially reduces the amount ofthermal conduction between the terminals (as compared to when thethermal switch 262 is closed).

The system 200 further includes a reservoir 270 that is coupled to theheat exchanger 230 via tubing 272. The reservoir 270 occupies some ofthe otherwise unused space within the vessel 202. Alternatively, thevessel 202 can have the design modified to accommodate the reservoir270. In one embodiment, the reservoir has a volume of at least 2 liters,and in another embodiment, at least 20 liters, at least 50 liters, atleast 101 liters or even larger. The system 200 also includes afill/vent line 274 that can be used to initially charge the reservoir270 with a cryogen. In an alternative embodiment, the reservoir 270 canbe used in conjunction with or replaced by a set of reservoirs. Inanother alternative embodiment, the fill/vent line 274 can be replacedby a separate fill line and a separate vent line. In still anotheralternative embodiment, more than one fill/vent line, fill line, ventline, or any combination thereof can be used.

After the system 200 is manufactured, it can be charged with a cryogen(for the buffer fluid) by flowing the cryogen through the fill/vent line274 to the reservoir 270. In one embodiment, the pressure within thereservoir 270 can be at least 0.5 atm, and in other embodiment, thepressure can be at least 1.5 atm, or even greater. At the same ordifferent time, the same or different cryogen (for the circulatingfluid) can be used to charge the heat transfer structure 220. Thecryogen(s) may be added to the system 200 at the place where the system200 is manufactured, at the final installation (e.g., in a laboratory, ahospital examination room, etc.), near the final installation (e.g., atthe loading dock of the facility having the laboratory, hospitalexamination room, etc.), or at nearly any location after themanufacturing and before final installation locations (e.g., at a heliumor liquefied gas storage facility).

Although not illustrated, other components, sub-systems, or anycombination thereof can be present in the system 200. For example, acomputer, a controller, or any combination thereof can be used tocontrol the system 200 when it is operating. The system 200 can includevalves, pumps, sensors, switches, regulators, or any combinationthereof, which are not illustrated, to allow for the proper operation ofthe system 220. In addition, tubing or other connections can be made.For example, more than one piece of tubing may couple the reservoir 270to the heat exchanger 230. One piece of tubing may be connected betweenthe reservoir 270 and the heat exchanger 230 to allow gaseous cryogen toflow from the reservoir 270 to the heat exchanger 230, and another pieceof tubing (not illustrated) may be connected at a point near the bottomof the heat exchanger 230 and to a point at a lower elevation in thereservoir 270 to allow liquid cryogen to flow from the heat exchanger230 to the reservoir 270. In a particular embodiment, the liquid levelsof the liquid cryogen 238 within the heat exchanger 230 and within thereservoir 270 are at substantially the same elevation.

Alternative embodiments can be used. For example, the reservoir 270 maybe external to the vessel 202 and may be connected or disconnected asneeded or desired. The heat transfer structure 220 can include more thanone cooling loop. In a particular embodiment, the heat transferstructure 220 can include separate loops that can include the samecryogenic fluid or different cryogenic fluids as compared to each other.

The heat exchanger 250 can be replaced by a plurality of heatexchangers, the thermal switch 262 can be replaced by a plurality ofthermal switches, the coldhead 244 can be replaced by a plurality ofcoldheads, or any combination thereof. Many different configurations ofcoldhead-heat exchanger-thermal switch combinations are possible. Aplurality of coldheads may be thermally connected to a single heatexchanger or a plurality of heat exchangers. Alternatively, the coldhead244 may be thermally connected to a plurality of heat exchangers. In oneembodiment, the thermal coupling may be accomplished by a permanentthermal connection or a thermal switch. The heat exchanger(s) andthermal switch(es) may correspond to a one-to-one, one-to-many,many-to-one, or many-to-many configuration, or a combination ofdifferent configurations.

In still other embodiment, the concepts can be extended to othercryogenic systems, such as high-temperature superconductors. Ifhigh-temperature superconductors are present, the selection of potentialcryogens that can be used can increase. For example, N₂ can be used.Further, the concepts described herein are not limited to onlyelectronic applications. The system can be used where an object, achamber, etc. is to be taken to a cryogenic temperature (e.g., testingphysical properties when a material is at a cryogenic temperature).

The operation of the system 200 can include three or more portions. Theoperation as described below is directed to a system that includes asuperconductor, such as superconducting element 212. Before starting thesystem, substantially no current is flowing within or through thesuperconducting element 212. The heat transfer structure 220 has thecirculating fluid disposed within. The reservoir 270, the heat exchanger230, or both have the buffer fluid disposed therein. No liquid cryogenmay be present or may only be within the reservoir 270, the heatexchanger 230, or both before starting the system.

During a first portion, initial cooling will begin, and the vessel 202will be evacuated, if evacuation has not yet occurred. The vessel 202can be evacuated to a very low pressure during a single stage or morethan one stage. If the vessel 202 included air before starting, thevessel 202 can be evacuated by the roughing pump and backfilled with thesubstantially dry inert gas for a plurality of times to removesubstantially all moisture within the vessel 202 before activating thediffusion or cryogenic pump. The vessel 202 can be finally taken to apressure as previously described.

With respect to the initial cooling, the coldhead 244 is activated. Ifthe heat exchanger 250 and thermal switch 262 are present, the thermalswitch 262 can be closed to accelerate cooling of the system 200. Withinthe wetsock 242, gaseous cryogen 236 is condensed by the coldhead 244 toform the liquid cryogen 238 that can collect within the heat exchanger230. Some of the liquid cryogen 238 may flow into the reservoir 270. Asthe temperature within the heat exchanger 230 decreases, the circulatingfluid disposed within the portion 234 of the heat transfer structure 220becomes denser, and the denser circulating fluid flows to the portion214 that is thermally connected or coupled to the object to be cooled,which is the superconducting element 212. Heat is transferred fromobject being cooled (e.g., superconducting element 212) to thecirculating fluid disposed within the heat transfer structure 220. Therecirculation fluid becomes less dense and flows from the portion 214 tothe portion 234 within the heat transfer structure. If naturalconvection is used, the circulating fluid will continue to flow until atemperature difference between the portions 214 and 234 no longer ismaintained. If forced convection is used for the heat transfer structure220, a pump or other equipment can be activated, so that the circulatingfluid circulates within the heat transfer structure 220.

During a second portion, after the initial cooling, if present, thethermal switch 262 is opened, so that heat exchangers 230 and 250 are nolonger thermally connected to each other. During the second portion, theheat exchanger 250 may not accelerate and could inhibit further coolingwithin the heat exchanger 230. The thermal switch 262 can be openedafter the heat exchanger 230 reaches a predetermined temperature, orafter a predetermined time, using another suitable criterion, or anycombination thereof. When temperature is used, the thermal switch may beopened when the temperature within the heat exchanger 250 is operatingat a temperature less than 90 K, less than 50 K, or less than 20 K. Ifthe system 200 does not include the thermal switch 262 or if the thermalswitch 262 was not closed during the first portion, the second portioncan be omitted.

During a third portion, the system 200 is further cooled so that theobject to be cooled (e.g., superconductor element 212) is at or near asteady state temperature. The steady state temperature depends on theselection of the cryogens used. In one embodiment, the steady statetemperature is about the boiling point of the liquid cryogen 238disposed within the heat exchanger 230. At steady state, the circulatingfluid can be in a single phase state, and the buffer fluid can be in atleast two phase states (liquid and gas).

After the superconducting element 212 is at or near the steady statetemperature, the superconducting element 212 can be activated. In oneembodiment, the superconducting element 212 includes a superconductingcoil, and the superconducting coil can be taken to its typical operatingstate (e.g., at field). After the superconducting coil is at its typicaloperating state, a patient or other specimen can be placed into ananalyzing region and be analyzed.

The system 200 does not need to be recharged with a significantly largevolume of cryogen after a quench or other undesired condition. Thus, thecost and difficulty related to recharging a system with a cryogen,particularly a cryogen (e.g., He, H₂, Ne) used for a low-temperaturesuperconductor, can be obviated altogether or at least delayed for arelatively long period of time (e.g., years, after multiple quenches orother undesired conditions would have occurred, etc.). Alternatively, iflost cryogen would be replaced, additional gaseous cryogen can be addednear room temperature and cooled by the system to the operatingtemperature, state, and pressure.

After the quench or other undesired condition no longer exists, thesystem 200 can be taken to its steady state temperature as previouslydescribed, and then the superconducting element 212 can be activated.

In addition to the ability to withstand faults or other undesiredconditions without having to recharge the system 200 with a cryogen, thesystem 200 and its use has other advantages. The initial cryogeniccharging of the system 200 can take place at nearly any time. Theability to charge the system 200 with a cryogen at any state ortemperature earlier in the process and not having to recharge the system200, particularly following a fault or other undesired condition, at thefinal installation location can obviate the need to have a costly ordifficult apparatus or method for getting a cryogen to the system 200after it is installed.

The ability to use a liquid cryogen allows the system 200 to be cooledsignificantly faster as compared to conventional conductive cooling. Thesystem 200 can use natural or forced convention to aid in cooling. Whenthe optional heat exchanger 250 and thermal switch 262 are used, thecooling can be even faster.

The coldhead 244 can include a bellows and seal (not illustrated)coupled to the wetsock 242 or other portion of the vessel 202. Thebellows and seal can allow the coldhead 244 to be moved to allow foreasier servicing without compromising the vacuum space in chamber 202.

The cryogen for the buffer fluid, circulating fluid, or both can beadded during operation, if needed or desired. The cryogen can flowthrough the fill/vent line 274 at a relatively low temperature or evennear room temperature (e.g., 20-25 C) to the reservoir 270. Whenoperating, the newly added cryogen may be able to have its temperaturelowered to the operating state (e.g., boiling point of the cryogen)relatively quicker. Thus, the system 200 allows for more flexibility ifadditional cryogen is to be added. Regarding the heat transfer structure220, the cryogen can be added to the return line (line where cryogenflows from the superconducting element 212 to the heat exchanger 230) orto the heat exchanger 230, such that the cryogen will be at or near theboiling point of the material used for the buffer fluid before the newlyadded cryogen reaches portion 214 of the heat transfer structure 220.

Many different aspects and embodiments are possible. Some of thoseaspects and embodiments are described below. After reading thisspecification, skilled artisans will appreciate that those aspects andembodiments are only illustrative and do not limit the scope of thepresent invention.

In a first aspect, a system can include a coldhead, a first heatexchanger operable to receive a first cryogenic fluid and coupled to thecoldhead, a chamber designed to be operated at a cryogenic temperature.The system can also include a heat transfer structure including a closedloop and further includes a first portion disposed within the first heatexchanger and a second portion disposed within the chamber. The closedloop can be operable to contain a second cryogenic fluid that would bedisposed therein, and the first heat exchanger can be designed such thatthe first cryogenic fluid and the second cryogenic fluid would be spacedapart from each other.

In one embodiment of the first aspect, the system is designed such thatthe first cryogenic fluid would have a different phase state as comparedto the second cryogenic fluid, the system is designed such that thefirst cryogenic fluid would have a different composition as compared tothe second cryogenic fluid, or any combination thereof. In anotherembodiment, the first heat exchanger is operable to receive the firstfluid cryogen as a liquid cryogen from the coldhead. In still anotherembodiment, the system further includes a wetsock coupled to thecoldhead, wherein the coldhead is disposed within the wetsock. In yetanother embodiment, the system further includes a reservoir coupled tothe first heat exchanger, wherein the reservoir has a capacitysufficient to receive spillover from the first cryogenic fluid during atypical operating state.

In a further embodiment of the first aspect, the system further includesa second heat exchanger, wherein the second heat exchanger is coupled tothe coldhead and the first heat exchanger. In a particular embodiment,the system further includes a thermal switch including a first terminaland a second terminal, wherein the first terminal is coupled to thefirst heat exchanger, and the second terminal is coupled to the secondheat exchanger.

In a second aspect, a superconducting system can include a chamber, asuperconducting element disposed within the chamber, a first heatexchanger disposed within the chamber, and a heat transfer structuredisposed within the chamber and thermally coupled to the superconductingelement and the first heat exchanger.

In one embodiment of the second aspect, the first heat exchanger isoperable to cool a first fluid with a second fluid, wherein the firstfluid includes gaseous He, and the second fluid includes gaseous He andliquid He. In another embodiment, the first heat exchanger lies at anelevation higher than a lowest point of the heat transfer structure. Ina particular embodiment, the heat transfer structure is configured toallow a fluid to flow within the heat transfer structure by naturalconvection when the superconducting system would be operating at steadystate.

In a further embodiment of the second aspect, the superconducting systemfurther includes a coldhead operable to condense a first gaseous cryogeninto a liquid cryogen, and a wetsock coupled to the first heatexchanger, wherein the first heat exchanger is operable to receive theliquid cryogen when the coldhead would be operating. In a particularembodiment, the superconducting system further includes a second heatexchanger, a thermal switch connected to the first heat exchanger andthe second heat exchanger, and a reservoir connected to the first heatexchanger.

In a third aspect, a method of using a system can include providing afirst cryogenic fluid, cooling a second cryogenic fluid with the firstcryogenic fluid, wherein the first cryogenic fluid and the secondcryogenic fluid remain spaced apart from each other, flowing the secondcryogenic fluid disposed within a heat transfer structure that iscoupled to a cooled object, and cooling the cooled object to a cryogenictemperature using the second cryogenic fluid.

In one embodiment of the third aspect, the method further includescondensing a gaseous cryogen within the first cryogenic fluid into aliquid cryogen. In a particular embodiment, cooling the second cryogenicfluid includes contacting the heat transfer structure with the liquidcryogen. In another embodiment, cooling the cooled object is performedwhile a superconducting element is disposed within the chamber.

In a further embodiment of the third aspect, the method further includesoperating the superconducting element, wherein operating thesuperconductor element is performed while a first pressure within thechamber is less than atmospheric pressure, and flowing the secondgaseous cryogen is performed at a second pressure less than atmosphericpressure. In a particular embodiment, the first pressure is at leastthree orders of magnitude lower than the second pressure. In anotherparticular embodiment, the method further includes closing a thermalswitch between a first heat exchanger and a second heat exchanger. In amore particular embodiment, the method further includes opening thethermal switch after flowing the second gaseous cryogen before thesuperconducting element is in its typical operating state.

In another embodiment of the third aspect, the method further includesflowing the first cryogenic fluid from a reservoir to a heat exchanger.In yet another embodiment, the method further includes flowing a liquidcryogen from the heat exchanger to the reservoir.

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed is not necessarily the order inwhich they are performed.

The illustrations of the embodiments described herein are intended toprovide a general understanding of the structure of the variousembodiments. The illustrations are not intended to serve as a completedescription of all of the elements and features of apparatus and systemsthat utilize the structures or methods described herein. Many otherembodiments may be apparent to those of skill in the art upon reviewingthe disclosure. Other embodiments may be utilized and derived from thedisclosure, such that a structural substitution, logical substitution,or another change may be made without departing from the scope of thedisclosure. Additionally, the illustrations are merely representationaland may not be drawn to scale. Certain proportions within theillustrations may be exaggerated, while other proportions may beminimized. Accordingly, the disclosure and the figures are to beregarded as illustrative rather than restrictive.

One or more embodiments of the disclosure may be referred to herein,individually or collectively, by the term “invention” merely forconvenience and without intending to voluntarily limit the scope of thisapplication to any particular invention or inventive concept. Moreover,although specific embodiments have been illustrated and describedherein, it should be appreciated that any subsequent arrangementdesigned to achieve the same or similar purpose may be substituted forthe specific embodiments shown. This disclosure is intended to cover anyand all subsequent adaptations or variations of various embodiments.Combinations of the above embodiments, and other embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the description.

The Abstract of the Disclosure is provided to comply with 37 C.F.R.§1.72(b) and is submitted with the understanding that it will not beused to interpret or limit the scope or meaning of the claims. Inaddition, in the foregoing Detailed Description, various features may begrouped together or described in a single embodiment for the purpose ofstreamlining the disclosure. This disclosure is not to be interpreted asreflecting an intention that the claimed subject matter requires morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter may be directed toless than all of the features of any of the disclosed embodiments. Thus,the following claims are incorporated into the Detailed Description,with each claim standing on its own as defining separately claimedsubject matter.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

It is to be appreciated that certain features are, for clarity,described herein in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures that are, for brevity, described in the context of a singleembodiment, may also be provided separately or in any subcombination.Further, reference to values stated in ranges includes each and everyvalue within that range.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover any andall such modifications, enhancements, and other embodiments that fallwithin the scope of the present invention. Thus, to the maximum extentallowed by law, the scope of the present invention is to be determinedby the broadest permissible interpretation of the following claims andtheir equivalents, and shall not be restricted or limited by theforegoing detailed description.

1. A system comprising: a coldhead; a first heat exchanger operable toreceive a first cryogenic fluid and coupled to the coldhead; a vesseldesigned to be operated at a cryogenic temperature; and a heat transferstructure including a closed loop and further including a first portiondisposed within the first heat exchanger and a second portion disposed,wherein: the closed loop is operable to contain a second cryogenic fluidthat would be disposed therein; and the first heat exchanger is designedsuch that the first cryogenic fluid and the second cryogenic fluid wouldbe spaced apart from each other.
 2. The system of claim 1, wherein: thesystem is designed such that the first cryogenic fluid would have adifferent phase state as compared to the second cryogenic fluid; thesystem is designed such that the first cryogenic fluid would have adifferent composition as compared to the second cryogenic fluid; or anycombination thereof.
 3. The system of claim 1, wherein the first heatexchanger is operable to receive the first fluid cryogen as a liquidcryogen from the coldhead.
 4. The system of claim 1, further comprisinga wetsock coupled to the coldhead, wherein the coldhead is disposedwithin the wetsock.
 5. The system of claim 1, further comprising areservoir coupled to the first heat exchanger, wherein the reservoir hasa capacity sufficient to receive spillover from the first cryogenicfluid during a typical operating state.
 6. The system of claim 1,further comprising a second heat exchanger, wherein the second heatexchanger is coupled to the coldhead and the first heat exchanger. 7.The system of claim 6, further comprising a thermal switch including afirst terminal and a second terminal, wherein: the first terminal iscoupled to the first heat exchanger; and the second terminal is coupledto the second heat exchanger.
 8. A superconducting system comprising: avessel; a superconducting element disposed within the vessel; a firstheat exchanger disposed within the vessel; and a heat transfer structuredisposed within the vessel and thermally coupled to the superconductingelement and the first heat exchanger.
 9. The superconducting system ofclaim 8, wherein the first heat exchanger is operable to cool a firstfluid with a second fluid, wherein the first fluid includes gaseous He,and the second fluid includes gaseous He and liquid He.
 10. Thesuperconducting system of claim 8, wherein the first heat exchanger liesat an elevation higher than a lowest point of the heat transferstructure.
 11. The superconducting system of claim 10, wherein the heattransfer structure is configured to allow a fluid to flow within theheat transfer structure by natural convection when the superconductingsystem would be operating at steady state.
 12. The superconductingsystem of claim 8, further comprising: a coldhead operable to condense afirst gaseous cryogen into a liquid cryogen; and a wetsock coupled tothe first heat exchanger, wherein the first heat exchanger is operableto receive the liquid cryogen when the coldhead would be operating. 13.The superconducting system of claim 12, further comprising: a secondheat exchanger; a thermal switch connected to the first heat exchangerand the second heat exchanger; and a reservoir connected to the firstheat exchanger.
 14. A method of using a system comprising: providing afirst cryogenic fluid; cooling a second cryogenic fluid with the firstcryogenic fluid, wherein the first cryogenic fluid and the secondcryogenic fluid remain spaced apart from each other; flowing the secondcryogenic fluid disposed within a heat transfer structure that iscoupled to a cooled object; and cooling the cooled object to a cryogenictemperature using the second cryogenic fluid.
 15. The method of claim14, further comprising condensing a gaseous cryogen within the firstcryogenic fluid into a liquid cryogen.
 16. The method of claim 15,wherein cooling the second cryogenic fluid comprises contacting the heattransfer structure with the liquid cryogen.
 17. The method of claim 14,wherein cooling the cooled object is performed while a superconductingelement is disposed within the vessel.
 18. The method of claim 17,further comprising operating the superconducting element, wherein:operating the superconductor element is performed while a first pressurewithin the vessel is less than atmospheric pressure; and flowing thesecond gaseous cryogen is performed at a second pressure less thanatmospheric pressure.
 19. The method of claim 18, wherein the firstpressure is at least three orders of magnitude lower than the secondpressure.
 20. The method of claim 18, further comprising closing athermal switch between a first heat exchanger and a second heatexchanger.
 21. The method of claim 20, further comprising opening thethermal switch after flowing the second gaseous cryogen before thesuperconducting element is in its typical operating state.
 22. Themethod of claim 14, further comprising flowing the first cryogenic fluidfrom a reservoir to a heat exchanger.
 23. The method of claim 22,further comprising flowing a liquid cryogen from the heat exchanger tothe reservoir.